Trimeric G proteins regulate the cytosol-induced redistribution of Golgi enzymes into the endoplasmic reticulum

Abstract

Streptolysin O-permeabilized cells incubated with a high concentration (5-10 mg/ml) of cytosolic proteins and ATPgenerating system exhibit redistribution into the endoplasmic reticulum (ER) of Golgi integral proteins (mannosidase II, galactosyltransferase, TGN 38), detected by immunofluorescence. In addition, mannosidase II is detected in the ER of cells exposed to a high concentration of cytosolic proteins and processed for immunolectron microscopy by immunoperoxidase. The redistribution process requires ATP and is not affected by previous microtubule depolymerization. Ultrastructural observations indicate that Golgi disassembly occurs by budding of coated vesicles. This stage of the process is inhibited by GTPgS, AlF(3-5), transducin bg subunits, and mastoparan, indicating the involvement of trimeric G proteins. At a later stage, vesicles lose their coats and fuse with the ER. This part of the process does not occur in cells incubated at either 15°C or 20°C, or exposed to N-ethylmaleimide. In cells treated with either cholera or pertussis toxin Golgi redistribution into the ER shows a 50-fold lower requirement for cytosolic factors than in untreated cells. These data suggest a regulatory role for both as and ai trimeric G proteins in the normal Golgi-ER retrograde transport taking place in intact cells